Field of the Invention
The present invention relates to a forming mold for a gasket and a method of manufacturing the gasket according to the sealing technology.
Description of the Conventional Art
As one kind of an endless-shaped gasket, there has been conventionally known widely an O-ring which is formed into a planar circular ring shape, and the O-ring is formed into various sizes in correspondence to a product specification.
In the case of forming a large-diameter O-ring in which a diameter goes beyond, for example, 1600 mm, a size of a used forming mold comes to 2000 mm in one side if it is intended to integrally form the O-ring while keeping a product shape as it is, so that a manufacturing facility is extremely enlarged in size.
Further, there has been developed a method of carrying out a joining work after divisionally forming one O-ring in a circumferential direction, however, according to this method, it takes a lot of labor hour and time for manufacturing, and concavity and convexity is generated in a joint section of the formed product, so that a lack of strength tends to be generated.
Taking the above problem into consideration, the applicant of the present invention has previously proposed a forming mold 51 shown in FIG. 3 (refer to Japanese Unexamined Patent Publication No. 2007-301874).
More specifically, the forming mold 51 is a forming mold for integrally forming an endless-shaped gasket, and has a plurality of forming sections 52 in which two forming grooves 53 and 54 aligned in parallel so as to be adjacent to each other are arranged spirally, each of the spiral forming grooves 53 and 54 has a reversing section 55 in an inner end portion thereof and is provided with a structure obtained by connecting outer end portions thereof to each other in series. According to the forming mold 51, it is possible to make a planar shape of the forming mold for integrally forming the large-diameter gasket as small as possible, thereby downsizing a manufacturing facility. Further, it is possible to suppress generation of any lack of strength in the joint section without a lot of labor hour and time for manufacturing since the gasket is integrally formed.
However, according to the forming mold 51, there may be generated in the gasket which is the formed product a curling shape (a curling shape due to forming, that is, a meandering shape left partially on a circumference without forming the prescribed product shape of the gasket after taking the gasket out of the mold), in an S-shaped reversing section 55 which is positioned in a center portion of the spiral shape. There is a possibility that deformation is left in a part of the gasket after a correcting treatment of the curling shape.